1. Technical Field
Exemplary embodiments relate to memory devices, and more particularly to a memory system, a memory device, a memory controller and methods of operating the same.
2. Discussion of the Related Art
A volatile memory device, such as a dynamic random access memory (DRAM), may perform a refresh operation to retain data stored in memory cells. If a memory cell has a retention time shorter than a refresh period defined in the standard, a row of memory cells including the memory cell should be replaced with a row of redundancy cells. As the size of a memory cell shrinks, the number of memory cells having retention times shorter than the refresh period increases. Accordingly, the number of rows of redundancy cells should be increased in a conventional volatile memory device.